The goal of the project is to develop intervention methods that improve long-term weight loss. Obesity is a major health problem in the United States. It affects more than 50 million Americans, causes significant morbidity (e.g., diabetes and hypertension), and contributes to increased cardiovascular mortality. Unfortunately, however, current treatment approaches for obesity are not successful in producing long-term weight loss. Prior research suggests that exercise behavior is the strongest predictor of long-term weight loss, but the level of exercise associated with successful long-term weight loss appears to be much higher than that usually prescribed in weight loss programs. The aim of the present study is, therefore, to test the effects on long-term weight loss of an enhanced exercise intervention that includes a high exercise goal (2500 kcal/wk rather than the usual 1000 kcal/wk) and strong behavioral methods to promote adherence to this goals. The behavioral strategies include individualized exercise prescriptions, validating feedback on exercise, therapist-implemented cues and incentive, and a social support manipulation that incorporates family and friends into the program to enhance natural cues and reinforcers for exercise. Subjects (N=180) will be randomized to either standard behavioral treatment or the enhanced exercise intervention. All subjects and social support partners will be treated for 18 months and assessed at baseline, 6, 12, 18, and 30 months. Primary outcomes will be weight loss at 18 months and 30 months. The proposed research is important because it explicitly focuses on long-term weight loss, the number one problem in the treatment of obesity. It seeks for the first time to determine whether targeting a high exercise level and providing strong behavioral strategies to help participants achieve this goal will be effective in improving the long- term results of obesity treatment. If effective, the intervention methodologies can be adapted to clinical settings. Use of social support partners may also increase the population outreach of behavioral weight control programs.